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Recent advances in self-frequency-doubling crystals

Benm

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Sometimes these things take time and then suddenly pick up speed and commercial application. The first 532 nm light from a doubler crystal was in the 90s, and this was literally a crystal in front of a pulsed 1064 nm lab laser.

I'm not sure what the efficiency of that system was, but i'm sure it was really low, just a slight shimmer of green from an IR laser that had enough punch to break down air if you shot it through a lens.

It took maybe 20 years to get laser pointers with intra-cavity doubling and continous operation to be available for a few dollars each with more (average) optical output than that original setup had.

DPSS may help us reach wavelengths currently hard to achieve, but aslo far better optical specs for wavelengths that are readily available today. The only major downside with them is that they are very finicky - you need to get the optical path and pumping wavelenght exactly right, and even then performance is very temperature dependent.
 

logsquared

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Sometimes these things take time and then suddenly pick up speed and commercial application. The first 532 nm light from a doubler crystal was in the 90s, and this was literally a crystal in front of a pulsed 1064 nm lab laser.
Laserscope had a 20W KTP intra cavity 532nm laser in the mid to late 80's. Im sure they were doubling the yag 1064 line in the 70's.
 

paul1598419

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My Walter Koechner book says KTP was difficult to grow in large pieces in the 1980s. I got the impression that only very small crystals were available back then. It says crystals were limited in size to a few mm, but by 1989 they had ones as large as a cm^3.
 
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steve001

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Two possible crystals that might be the ones used to create yellow lasers offered by Optlasers.

Self-frequency-doubled vibronic yellow Yb: YCOB laser at the wavelength of 570 nm

Qiannan Fang, Dazhi Lu, Haohai Yu, Huaijin Zhang, Jiyang Wang

Optics letters 41 (5), 1002-1005, 2016<br>

A watt-level self-frequency-doubled yellow laser at the 570 nm wavelength was realized by taking advantage of the vibronic emission of a Yb^ 3+ doped calcium yttrium oxoborate (Yb: YCOB) crystal cut along the optimized direction out of the principal planes with the maximum effective nonlinear coefficient. Fluorescence spectroscopic properties of Yb: YCOB were studied, which showed that it had broad and anisotropic vibronic emission with a small peak at∼ 1130 nm. By suppressing the electronic emission,
and a crystal known as Yb:SVAP
 

logsquared

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My Walter Koechner book says KTP was difficult to grow in large pieces in the 1980s. I got the impression that only very small crystals were available back then. It says crystals were limited in size to a few mm, but by 1989 they had ones as large as a cm^3.
That probably explains way the KTP in my Lasercope (built 1988 iirc) was so tiny. Alignment was uber critical. If the intra cavity beam touched the wall of the KTP it was game over and the KTP would crack. Still amazes me how much power went through such a tiny crystal.
 

paul1598419

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Yeah, if you got anywhere near a watt out, that is very high power density in the KTP. I don't know how large the crystals are in my 1300 mW 532 labby because I won't take a perfectly good working laser apart just to satisfy my curiosity. It goes against my motto, "If it ain't broke, don't fix it."
 

CurtisOliver

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Two possible crystals that might be the ones used to create yellow lasers offered by Optlasers.


and a crystal known as Yb:SVAP
Yep, these are the options I came up with a while back. That and Yb:YAB.
Obviously I can't be certain, but I'm fairly confident both the 565 and 575's are Yb doped. As said before the pumping wavelength has been confirmed to be 976nm which is perfect for pumping Yb efficiently.
But it still isn't possible to narrow down which it is yet. I still believe that it is an entirely new Yb doped crystal, as these lasers are new and undocumented. And crystal production is difficult still. Doesn't explain however why they are so cheap. When the crystals are produced properly they must be pretty large in order to allow tiny crystals to go so cheaply.
 

steve001

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Yep, these are the options I came up with a while back. That and Yb:YAB.
Obviously I can't be certain, but I'm fairly confident both the 565 and 575's are Yb doped. As said before the pumping wavelength has been confirmed to be 976nm which is perfect for pumping Yb efficiently.
But it still isn't possible to narrow down which it is yet. I still believe that it is an entirely new Yb doped crystal, as these lasers are new and undocumented. And crystal production is difficult still. Doesn't explain however why they are so cheap. When the crystals are produced properly they must be pretty large in order to allow tiny crystals to go so cheaply.
Maybe this narrows it down a bit more? What also remains unknown is are there or can these types of lasers using these types of crystals work without using a fiber optic? That's what all of the diagrams I've veiwed so far show.
We report widely tunable infrared and self-frequency-doubled operation in ytterbium-doped yttrium aluminum borate (Yb:YAB). In the infrared, tuning has been obtained between 1016 and 1090 nm and also near 1125 nm. A tuning range at the 1-W level of 55 nm has been obtained. As a self-frequency-doubled laser, green output powers of 65 mW at 510 nm and over 450 mW at 530 nm have been demonstrated with a maximum diode-to-green conversion efficiency of 5%. Yb:YAB has been shown to cover the wavelengths of the copper-vapor (510 nm), argon-ion (514 nm), doubled Nd:YAG (532 nm), green HeNe (543 nm), and the doubled Yb:Sr5(VO4)3F laser in the visible (~565 nm).
https://www.researchgate.net/public...on_the_self-frequency-doubling_material_YbYAB
Widely tunable yellow-green lasers based on the self-frequency-doubling material Yb:YAB | Request PDF. Available from: https://www.researchgate.net/public...on_the_self-frequency-doubling_material_YbYAB [accessed Aug 03 2018].
 

paul1598419

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Because the pump wavelength is so high, I don't think this crystal will pan out as our 565nm or 575nm lasers. The pump wavelength is <980nm and by how much, I'm not entirely sure yet. But, you are correct that the fiber optically pumped crystals are not candidates either.
 

CurtisOliver

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The crystals were already found to be be pumped by 976nm and I have already found out that Yb doped crystals work at that wavelength. They are also sfd meaning they have transition lines that self double their frequency.
 

logsquared

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Yeah, if you got anywhere near a watt out, that is very high power density in the KTP. I don't know how large the crystals are in my 1300 mW 532 labby because I won't take a perfectly good working laser apart just to satisfy my curiosity. It goes against my motto, "If it ain't broke, don't fix it."
28Watts was the max I could juice of her:eg: this was 20 years ago but i think the KTP was 2mmX2mmX5mm:beer::beer:
 

paul1598419

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The crystals were already found to be be pumped by 976nm and I have already found out that Yb doped crystals work at that wavelength. They are also sfd meaning they have transition lines that self double their frequency.
Nothing I said contradicts that this could be Yb doped. Only that the specific crystal in steve's paper is likely not a candidate. The pump wavelength for it was too high. There are many possible crystals that could be Yb doped and some have not been shown here yet.
 
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Benm

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Laserscope had a 20W KTP intra cavity 532nm laser in the mid to late 80's. Im sure they were doubling the yag 1064 line in the 70's.
Oh, i meant to say the first time i'd seen it with my own eyes was in the early 90s, not that it wasn't possible or done before that.

As for other wavelengths: Nd:YAG has a 946 nm line that can be selectively lased with mirror coatings, and doubled to 473nm. Those lasers are commercially available though usually far more expensive than the 532 nm ones for a given power level.

Beyond that there are little remotely affordable systems though, perhaps the 671 nm red, but given the long wavelength and hence low visibility per mW, is not desirable for any visual effects.

There are a couple of interesting wavelengths possible in the range between 532 and 671, but they are to this point too expensive or inefficient to be viable. That might change if there is a good commercial application for them though :)
 

CurtisOliver

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Nothing I said contradicts that this could be Yb doped. Only that the specific crystal in steve's paper is likely not a candidate. The pump wavelength for it was too high. There are many possible crystals that could be Yb doped and some have not been shown here yet.
It’s fine, I just skimmed your comment last night. I just reread it. :beer:
 

steve001

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Because the pump wavelength is so high, I don't think this crystal will pan out as our 565nm or 575nm lasers. The pump wavelength is <980nm and by how much, I'm not entirely sure yet. But, you are correct that the fiber optically pumped crystals are not candidates either.
Paul, I think those are lasing frequencies, not pump frequencies.
The crystals were already found to be be pumped by 976nm and I have already found out that Yb doped crystals work at that wavelength. They are also sfd meaning they have transition lines that self double their frequency.
I believe you are correct. These two are ytterbium lasers. I've included the title of the pdf but unable to link it. The pump frequency is 975 nm
"Self frequency doubling ytterbium laser".
 

paul1598419

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In post #24 are you saying the Yb:YAB crystal's lasing at 1016nm, 1090nm and 1125nm? I took the quote as those being the pump wavelengths and the lasing lines were 510nm and 530nm. It sure seems that those are pump wavelengths to me and much too high to be a candidate for the 575nm crystal or the 565nm crystal.
 




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